Factors affecting self-reported pain and physical function in patients with hip osteoarthritis

Objective: To determine the factors associated with self-reported pain and physical function in patients with hip osteoarthritis (OA). Design: Cross-sectional study. Setting: Rehabilitation clinic in a Finnish hospital. Participants: Participants with hip OA (N= 118; 35 men, 83 women; age, 66.7 +/- 6.5y; range, 55-80y). Interventions: Not applicable. Main Outcome Measures: Self-reported pain and self-reported disease-specific physical function were recorded by using the Western Ontario McMaster Universities Osteoarthritis Index. Self-reported generic physical function was analyzed by using the Finnish version of the RAND 36-Item Short-Form Health Survey. As listed in the International Classification of Functioning, Disability and Health model, the effects of personal factors (age, sex, education, depression, life satisfaction, smoking, years of sporting activities), pathophysiologic factors (radiologic score of hip OA, body mass index [BMI], comorbidities, duration of knee pain) and body functions and structures (measurement of leg extensor power, passive internal rotation and flexion of the hip joint, the six-minute walk test [6MWT], Timed Up & Go [TUG] test, ten-meter walk test, sock test) were analyzed. Results: The educational level (r=-.264, P<.001), comorbidities (r=.313, P<.001), and BMI (r=.252, P<.001) were identified as significant factors for self-reported disease-specific physical function as well as the educational level (r=.291, P<.001), life-satisfaction (r=-.319, P<.001), BMI (r=-.290, P<.001), and comorbidities (r=-.220, P<005) for the self-reported generic physical function. No direct relationship with the pain and psychologic factors was detected. The number of comorbidities and duration of knee pain and life satisfaction explained 22% of self-reported pain. The number of comorbidities, passive hip flexion, and the TUG test explained 20% of self-reported disease-specific physical function whereas the passive hip flexion, 6MWT, and educational level explained 25% of self-reported generic physical function. Conclusions: Educational level, life satisfaction, and number of comorbidities were identified as significant factors for both self-reported pain and physical functioning in hip OA. Performance measures are better predictors of physical function than pain in hip OA. Factors explaining disability and pain in hip OA are multidimensional and no single predicting factor was found to be superior to any other.